Radiotherapy and Nuclear Pharmacy Flashcards
what is a nuclide?
species of an atom with a specific number of protons and neutrons in its nucleus
what is radioactivity?
Spontaneous transformation of an unstable nucleus to a more stable nucleus with release of ionising radiation…
what is ionizing radiation?
radiation with enough energy that when it interacts with an atom it can remove bound electrons
what are the different radiation types?
Alpha – Positively charged He nuclei (2 protons + 2 neutrons)
Beta – Electrons
X-rays – EM radiation
Gamma – EM radiation
when is X-rays emitted?
X-rays are emitted when a target of heavy metal atoms is bombarded by energetic electrons
what is the charge of Alpha - a
mass of particles
penetrating power?
most damaging source?
positive
heavy particles
very low penetrating power
Most damaging source: Internal
what is the charge of Beta - B
mass of particles
penetrating power?
most damaging source?
negative
light particles
low penetrating power
most damaging source: internal
what is the charge of X-ray
mass of particles
penetrating power?
most damaging source?
neutral
no mass
very high penetrating power
most damaging source: external
what is the charge of Gamma- y
mass of particles
penetrating power?
most damaging source?
neutral
no mass
very high penetrating power.
most damaging source - External
what is the harmful effects of radiation?
harmful effects
- Depend on the energy and penetration power of the radiation as well as the time of exposure
- Include nausea, skin burns, loss of hair, sterility, cancer and even death
- Causes mutation in DNA
why do we use radiation
useful applications?
-Treatment of cancers
- Sterilising medical instruments and biomaterials
- Finding leaks
- Dating archaeological remains
- Generating electricity
what radiation is more internally damaging?
alpha-a
beta- b
what radiation is externally damaging
x-ray
gamma- y
what is half life?
radiopharmacuetical can be classified into long and short half life - what is it?
Half-life is the time it takes for the activity, or the amount of a radioactive isotope, to fall by half. The shorter the half life, the faster the isotope decays and the more unstable it is.
Radiopharmaceuticals can be classified into long and short half-life products.
Long half-life > 12 hrs
Short half-life < 12 hrs
what is the activity of a radioactive source?
The activity of a radioactive source is the number of nuclear transformations per unit time
1 Becquerel (Bq) is one disintegration per second (SI unit)
1 megabecquerel (1 MBq) = 106 Bq
1 kilobecquerel (1 kBq) = 103 Bq
1 curie (Ci) – 3.7×1010 disintegrations per second (dps)
1 millicurie (1 mCi) = 10-3 curie
1 microcurie (1 Ci) = 10-6 curie
1 nanocurie (1 nCi) = 10-9 curie
disintegration is an example of nuclear transformation
what is an absorbed dose?
Absorbed dose is the energy deposited per unit mass of material.
1 Gray (1 Gy) = 1 Joule of energy absorbed in 1 kg of material
Example: Typical radiation dose to kill bacteria (sterilisation) is 25 kGy.
what is a dose equivalent?
what is it measured it
Dose equivalent takes into account the variation in biological effectiveness of different radiations. It is measured in sieverts (1 Sv).
Dose equivalent = Absorbed dose × Quality factor (for particular radiation)
For gamma and beta radiation the quality factor is 1, so 1 Sv = 1 Gy
For alpha radiation the quality factor is 20, so 20 Sv = 1 Gy
alpha is more damaging than gamma as 20sv compated to 1sv
as it hits a particle it gives off energy immediately
gamma does this in a longer period of space and larger volume.
how can radiation be used diagnostically?
X-rays for diagnostics
how can radiation be used therapuetically?
External beam radiation for therapeutics
how can radiopharmaceuticals be used ?
Radiopharmaceuticals can also be used both therapeutically and diagnostically
what is radiopharmacy?
Radiopharmacy – manufacture and use of radioactive medicines
PET scans for diagnostics
Radionuclide therapy for therapeutics
what can you use therapeutically and diagnostically?
radiopharmacuetical and radiopharmacy?
what is the therapeutic use of radiation and what should be considered?
Deliver therapeutic doses of ionising radiation to specific disease sites with high specificity
Therapeutic radiopharmaceuticals – radio-labelled molecules
Important points to consider:
Specific targeting
Clearance of radioactivity from non-target radiosensitive tissues
Decay properties of the radionuclide
what is the mechanism of action of radiation?
(2 routes)
Radiation causes damage through two routes
- Direct damage (minor component)
DNA single (SSB) and double stranded breaks (DSB) (one double-stranded break per 25 single-stranded breaks) - Indirect damage (major component)
Hydrolysis of water which then reacts with cellular components
SSBs, DSBs, breakage of disulfide bridges in proteins
what are the three approaches of radiotherapy?
Radiation used to treat cancer
Three approaches:
1. External beam radiation
2.Sealed source radiotherapy – Brachytherapy
3. Unsealed source radiotherapy
what is external beam radiation?
when is higher and lower energy used?
Uses X-ray or gamma-ray radiation
Higher energy than for diagnostic purposes
Typical therapeutic energy 1-25 MeV (megaelectronvolts)
Typical diagnostic energy 20-150 KeV (kiloelectronvolts)
Lower energy range used to treat skin cancer
Higher energy range used to treat internal tumours including bladder, bowel, prostrate, lung and brain
what is sealed source radiotherapy (Brachytherapy)?
what is it used for?
what is the low dose rate and high dose rate?
Brachytherapy delivers radioisotopes sealed into capsules or wires
Radiation can escape, but radioisotope cannot move from site of action
Radioisotopes include iodine-125 or cesium-131.
Effective treatment for cervical, prostate, breast, oesophageal and skin cancer
low dose rate - up to 2Gy/h
high dose rate - over 12 Gy/h
what is low dose rate (LDR) branchytherapy (sealed) ?
what is it used to treat?
how long does it administer and exposure ?
Permanent implantation of radioactive seeds at site of action
Low dose of radiation administered over weeks or months
Typically use iodine-125 radionuclide (gamma-ray emission)
Used to treat prostate cancer
Low dose but long term exposure
what is high dose rate ( HDR) barchytherapy - sealed?
Temporary insertion of radioactive wires into site of action.
Can be combined with external beam radiotherapy.
Commonly use iridium-192 (gamma-ray emission)
High dose but short term exposure.
what is the difference between HDR and LDR?
LDR: Low dose but long-term exposure
over weeks or months
HDR: high dose but short term
temporary
what is unsealed source radiotherapy?
Use of radiopharmaceutical to localise at specific targets
Targeting due to properties of radiopharmaceutical (e.g. accumulation of iodine in thyroid) or administration route.
Patient takes oral or IV solution of radiopharmaceutical
Radionuclides used in UK include Iodine-131, Strontium-89 and Radium-223.
α or β emission usually required
what is the use of unsealed sources of radiotherapy?
More than 50% of patients with prostate, breast or lung cancer will develop painful bone metastases
Pain relief can be achieved by treatment with 89Sr-strontium chloride (β-radiation source).
When administered by the IV route, strontium is taken up by both the normal skeleton and, to a greater extent, skeletal metastases.
Irradiation of the tumour deposits by the 89Sr induces pain relief.
how can hyperthyroidism or thyroid cancer be treated?
Thyroid hormones are excessively released due to gland hyperfunction.
The cells need iodine to make the hormone, so they absorb any iodine found in the body.
131I-sodium iodide is often prescribed to damage cells that make thyroid hormone.
β-radiation source- reach site of action and penetrate - only to that organ not to the rest of the body.
Administration of radiopharmaceutical: Oral, either as a solution or in a capsule
Also used to treat thyroid cancer
how are radiopharmaceutical used for diagnostic different than those for therapeutics
Radiopharmaceutical used for diagnostics are different than those for therapeutics
Requires gamma emission, rather than α or β emission.
Short half-life – a few hours
Example: 99Tc – radionuclide with half-life 6 hrs and gamma emission.
how are radiopharmaceuticals administered?
Radiopharmaceutical are administered via IV.
how is radiopharmaceutical radiation detected?
The radiation is detected externally using a special scintillation detector, known as a gamma-camera.
what is Positron emission tomography (PET) scan?
how is it used to identify tumours?
Used to observe metabolic processes
Imaging technique using radiolabelled glucose – fludeoxyglucose
Contains 18F – a gamma source
Localisation can be used to assess glucose metabolism
Can be used to identify tumours due to an increased number of mitochondria in rapidly growing malignant masses
what is renal isotope scan (MAG3 Renogram)
Used to test renal function
Most common isotope - technetium Tc 99m mercaptoacetyltriglycine (99mTc-MAG3)
what is technetium?
when is it used?
Lightest chemical element with no stable isotope
99mTc – a metastable isotope of 99Tc
Most commonly used radioisotope used in medicine
Emits only gamma radiation
Prepared in water from [99mTcO4]-
Half life – 6 hours
On-site preparation and injection into the patient
what are examples of techetium?
The hexakis(alkyl isocyanide) complex of 99mTc(I) is an organometallic compound that has been successfully commercialised (Cardiolite)-
Since Cardiolite treatment is non-invasive, it has become the most important myocardial imaging method.
what are safety considerations of radiation?
Shielding
Plastic and metals like aluminium can shield beta-rays. Lead and tungsten can shield gamma-rays.
Distance
The radiation dose is inversely proportional to the square of the distance
Time
- Minimizing the time spent handling a radioactive source will reduce a radiation dose
